1. Field of the Invention
The invention relates to a method for supplying audio signals to a user wearing a hearing device at or in his ear, which comprises a sound attenuation portion for attenuating ambient sound before reaching the user's ear drum with the sound attenuation portion comprising a loudspeaker which is oriented towards the user's ear canal.
2. Description of Related Art
Such a hearing device may be a headphone or an earphone which is used for listening, for example, to music from a portable audio source, such as an MP3 player or a CD player. Usually such audio devices have a manual volume control which is operated by the user of the device according to the desired sound pressure level. One problem encountered with such devices is that the users of such portable audio devices, especially if young people, are tending to use the device at sound pressure levels which may create a hearing damage.
Active hearing protection devices comprise an active communication unit consisting of a microphone for capturing ambient sound, an audio signal processing unit and a loudspeaker for reproducing the sound captured by the microphone to the user's ear according to audio signal processing in the processing unit. Such active hearing protection devices, and also hearing aids, usually comprise some kind of level limitation which is based on the level of the input audio signals to the signal processing unit as provided by the microphone in order to limit the sound pressure level created by the loudspeaker to values which are not dangerous for the user's hearing.
U.S. Pat. No. 6,567,524 B1 relates to an earplug comprising a loudspeaker oriented towards the user's ear canal and a microphone connected to the user's ear canal via a sound passage in order to capture sound in the user's ear canal. According to one embodiment, the earplug may be used as a headphone coupled to a CD player in order to monitor the noise dose submitted from the headphones to the ear over time or in peaks. To this end, the earplug is provided with a signal processing unit.
DE 101 12 305 A1 relates to a hearing protection device comprising an earplug including a microphone oriented towards the user's ear canal for capturing sound in the ear canal and optionally a loudspeaker for providing audio signals to the user. The microphone is connected to a signal processing unit in order to measure in-situ the sound pressure level acting on the user's ear protected by the earplug. If the sound pressure level is found to be too high the device may take corresponding counter-measures in order to protect the user's hearing from damages. An example of such a counter measure is to act on the machine creating the noise.
It is also known to provide a hearing protection device, such as a headphone or an earplug, with a microphone oriented towards the user's ear canal for picking up sound in the ear canal, an audio signal processing unit and a loudspeaker oriented towards the user's ear canal for performing active noise reduction (ANR) wherein the loudspeaker is used for creating a phase-shifted anti-noise signal. Examples for such ANR hearing protection devices are given in WO 2005/046543 A1, U.S. Pat. No. 6,741,707 B2 and DE 101 17 705 A1.
U.S. Pat. No. 6,689,377 B2 relates to a method for measuring the acoustic attenuation provided by a customized earplug, wherein the earplug is provided with a sound bore extending from the outer side of the earplug to the inner end of the earplug, wherein a remote device is inserted into the outer end of the sound bore, which remote device comprises a first microphone oriented towards the sound bore and a second microphone oriented towards ambience, and wherein test sound is provided by an external loudspeaker. Both the loudspeaker and the remote device are connected to a computer unit on which a measurement program is run. The acoustic attenuation provided by the earplug is calculated from the sound level difference between the first microphone and the second microphone.
U.S. Pat. No. 5,577,511 relates to a method for measuring in-situ the acoustic attenuation provided by an earplug, wherein a probe tube extends through the earplug into the ear canal and wherein the outer end of the probe tube is connected to a first microphone, while a second microphone is provided at the ear for measuring sound pressure levels exterior to the ear canal as a reference microphone. The acoustic attenuation provided by the earplug is calculated from the difference of the sound levels measured by the first and the second microphone. The test sound for the measurement is the user's voice.
It is an object of the invention to provide for a method for supplying audio signals to a user by an car-worn hearing device comprising a sound attenuation portion with a loudspeaker, wherein the user's ear should be protected from damages. It is a further object to provide for a corresponding hearing system.